What's wrong with my friend's dog?

So she's a three year old caniche or bichon . And they found her in the street she couldn't see because her hair was covering her eyes and her owners gave her up . Although she's a three year old dog , she is not trained , doesn't even know the sit command , her owners also use screaming and glaring if she does something they don't like , she understand they are mad but the behaviour doesn't change . So , When I First met her and tried petting her she was just trembling . My friend and I then went to her room , the dog immediately hid under the bed , my friend told me she always does that and also she just scratches the floor when under the bed . Then my friend's parents came . Her mom was in the kitchen , and the dog was in the room with us , when I stood up and made my way to the kitchen , I didn't even enter yet .. she was barking at me like crazy she even scratched my leg with her teeth , not an official bite or anything like that , and then she went and hid under a table . My friend told me she has this habit of Surprise biting when you turn your back to her . Since then I couldn't be comfortable unless my friend will hold her because i knew she would bite me especially while next to her mom . Everytime i get close to her mom she starts growling at me , my friend's mom started scolding her and everything but it sure was not a way to raise her . Once again we finished eating , I stood up and she immediately run to me , barking at me like crazy . The dog is also a little agressive when they walk her . But she's literally a 3 years old dog who only eat and sleep , no activity , no training , and no correction to her bad behaviour , my friend literally laughs and will strat petting her unconsciously when she growls at me . But I can't seem to understand who fearful she was at the beginning . I'm sorry i wrote a lot , but i want to learn how to act around family dogs because i feel they have more issues than street dogs .